Tuning arrangement for concentric transmission line resonators



Feb. 3, 1948. A. MfGuREwl-rscl-l v 2,435,442

v TUNING ARRANGEMENT FH CONCENTRIC TRANSMISSION LINE RESONATORS Filed Dec. 2s, A1943 PLUNGER Posl'noN Inventor: A Anatole M. Gufewtsch,

His Attorney.

Patented Feb. 3, 1948 TUNING ARRANGEMENT FOR CONCENTRIC TRANSIVIISSION LINE RESONATORS Anatole M. Gurewitsch, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application December 23, 1943, Serial No. 515,345

4 Claims. 1

This invention relates to space resonant cavities of the concentric transmission line type, and in particular to arrangements for tuning such space resonant cavities.

It ls an object of my invention to provide a new and improved capacitive tuning arrangement for a concentric transmission line cavity resonator.

It is known that a space resonant cavity of the type comprising a tubular outer conductor and a centrally disposed inner conductor may be excited by means of suitable exciting means, such as an electron discharge device, to establish transverse electromagnetic waves between the inner and outer conductors. The frequency of the space resonant system thus dened may be adjusted by adjustment of the electrical length of the concentric transmission line. In the past, tuning plungers for adjusting the length of such lines and of the capacitive type have been employed, the tuning plunger usually consisting of a cylindrical sleeve interposed' between the inner and outer conductors and adjustably supported on one of these conductors. This sleeve forms a short section of transmission line with each of the conductors, the two sections of transmission line being connected in series for electromagnetic waves within the resonant cavity. It is apparent that in such a system the sections of transmission line formed by the plunger are of fixed length and, hence, optimum performance is obtained at only one frequency.

It is an object of my invention to provide a new and improved capacity tuning arrangement for a concentric transmission line resonator in which optimum operation of the resonator is obtained over a wide band of frequencies.

The features of the invention desired to be protected herein are pointed out in the appended claims. The invention itself, together with further objects and advantages, may best be understood by reference to the following description taken in connection with the drawing in which Fig. 1 is a longitudinal sectional view of a con- Acentric transmission line cavity resonator embodying one of my improved capacitive tuners; Fig. 2 is a cross-section of the capacitive tuner of Fig. 1 along the line 2 2; and Fig. 3 is a graph illustrating the tracking characteristic of the ultra high frequency arrangement of Fig. 1.

Referring to Figs. l and 2 jointly, there is shown an ultra high frequency space resonant system of the concentric transmission line type and comprising a tubular outer conductor I and a centrally disposed inner conductor II. Electromagnetic waves of the TEM, or transverse electromagnetic, type are established in the region between the conductors III and I I by any suitable exciting means, such as the electron discharge device I2 having its anode I3 connected to outer conductor I Il and its control electrode I4 connected for alternating currents to inner conductor II`. The outer conductor I0, preferably, is operated at ground potential and anode potential is supplied to anode I3 over a conductor I5. The cathode of the device may be connected to ground for alternating currents through bypass capacitor I6 and to a source of negative potential for unidirectional currents by means of a lead I l. The exact form of the electron discharge device employed for establishing electromagnetic waves between the conductors III and I I forms no part of the present invention and any suitable electron discharge device may be employed for this purpose. In the usual type of such systems, the electrodes themselves of the device I2 form a part of the boundary of the space resonant system.

The space resonant region between the conductors Ill and II may be adjusted to resonate at a desired frequency by means of a cup-like metallic plunger 20 slidably supported on inner conductor II and comprising a cylindrical sleeve portion 2I concentrically disposed between the inner and outer conductorsand extending longitudinally between these conductors, and an end wall 22 connecting the sleeve 2 I' to the conductor II. The longitudinal position of the plunger 20 along the concentric transmission line dened by the conductors I0 and II may be adjusted by any suitable adjusting means, one form of which is illustrated in the drawing as a pair of rods 23.

In the operation of capacitive tuning plunger 2 the sleeve 2l concentrically disposed between the conductors I0 and II forms therewith a pair of short sections of concentric transmission line, one of which is defined by the outer surface of sleeve 2| and the inner surface of outer conductor Ill and the other of which is defined by the inner surface of sleeve 2| and the outer surface of conductor II. These sections of transmission line are serially connected between the space resonant cavity to the left of the end wall 22 and the right-hand side of the end wall '22. The end wall 22 forms a short-circuit across the end of these serially connected sections of transmission line. From well-known considerations, it is apparent that optimum operation of a system employing a capacitive tuning plunger of this type is obtained at only one frequency, namely, the frequency at which the previously mentioned said inner conductor is varied, said means comprising a'pair of annular sleeves secured respectively to the inner surface of said outer conductor and the'outer surface of said inner conductor. said annularsleeves being substantially co-extengsive along said conductors and having opposed surfaces defining an annular region therebetween into which Asaid cylindrical sleeve is adapted to extend. Q

4. In combination, a space resonant systemicf the concentric transmission line type comprising a tubular outer conductor and a centrally posed inner conductor, and means for adjusting the resonance frequency of said system and for preventing the leakage of electromagnetic waves therefrom, said means comprising a pair of =v\ri'g`.ve reecting members attached respectively to the outer surface of said inner conductor andV the inner surface of said outer conductor, said niembers being substantially coextensive along said conductors, and an annular sleeve conductively ANATOLE M. GUREWITSCH.

REFERENCES CITED The following references are of record in the file of this patent:

'UNITED STATES PATENTS Name Date Roosenstein Apr. 1'1, 1934 Malter Aug. 29, 1939 Number 

